1. Field of the Invention
This invention relates to electronic devices such as integrated circuits and in particular to integrated circuit packages with enhanced thermal capabilities.
2. Description of the Prior Art
Present integrated circuit packages include ceramic and plastic ball grid arrays (BGAs) in which a ceramic or plastic substrate is electrically connected to an integrated circuit chip (die) using wire bonding, tape automated bonding (TAB), or controlled collapse chip connection ("C4" or "flip chip").
BGA packages are desirable because they are easier to surface mount on a printed circuit board (PCB) than fine pitch peripheral lead packages, such as quad flat pack (QFP) and dual in-line package arrangements, because the outer leads of BGA packages are distributed on the lower surface of the package, rather than being restricted to the package perimeter. Further, because BGA packages do not include peripheral leads, BGA packages take up less room on a host PCB, and may be closely spaced. This close spacing also allows for shorter interconnect lengths between packages, which results in improved electrical performance.
FIG. 1 is a cross-sectional view of a prior art BGA package 10 including an integrated circuit chip (die) 12 mounted on a substrate 14. Substrate 14 includes inner bonding pads 16 and outer bonding pads 18, and conductive lines (not shown) connecting inner bond pads 16 with outer bond pads 18. Wires 20 are connected between die bond pads 22, located on die 12, and inner bond pads 16. Die bond pads 22 are electrically connected to the integrated circuit fabricated on die 12. A plastic cover 24 is molded over die 12 and wires 20 for protection. Finally, solder balls 26 are connected to outer bond pads 18 for electrical connection to a host PCB (not shown).
A problem with prior art BGA packages is that they have relatively poor heat-dissipation characteristics. Typically, heat generated by the die is transmitted through the substrate and solder balls to an underlying printed circuit board. However, in peripheral array BGA packages in which the solder balls are placed around a perimeter of the substrate (that is, not underneath the die), heat generated by the die becomes trapped within the package causing a substantial temperature increase. This is a particular problem with peripheral BGA arrays when a plastic substrate is used because the die is completely encapsulated in plastic, which is a poor heat conductor.
It is therefore highly desirable to provide a BGA package which provides improved heat dissipation.